Co-occurrence of potentially preventable factors

Objective—To examine potentially preventable factors in human dog bite–related fatalities
(DBRFs) on the basis of data from sources that were more complete, verifiable, and accu-
rate than media reports used in previous studies.
Design—Prospective case series.
Sample—256 DBRFs occurring in the United States from 2000 to 2009.
Procedures—DBRFs were identified from media reports and detailed histories were com-
piled on the basis of reports from homicide detectives, animal control reports, and inter-
views with investigators for coding and descriptive analysis.
Results—Major co-occurrent factors for the 256 DBRFs included absence of an able-bodied
person to intervene (n = 223 [87.1%]), incidental or no familiar relationship of victims with
dogs (218 [85.2%]), owner failure to neuter dogs (216 [84.4%]), compromised ability of vic-
tims to interact appropriately with dogs (198 [77.4%]), dogs kept isolated from regular positive
human interactions versus family dogs (195 [76.2%]), owners’ prior mismanagement of dogs
(96 [37.5%]), and owners’ history of abuse or neglect of dogs (54 [21.1%]). Four or more of
these factors co-occurred in 206 (80.5%) deaths. For 401 dogs described in various media
accounts, reported breed differed for 124 (30.9%); for 346 dogs with both media and animal
control breed reports, breed differed for 139 (40.2%). Valid breed determination was possible
for only 45 (17.6%) DBRFs; 20 breeds, including 2 known mixes, were identified.
Conclusions and Clinical Relevance—Most DBRFs were characterized by coincident,
preventable factors; breed was not one of these. Study results supported previous recom-
mendations for multifactorial approaches, instead of single-factor solutions such as breed-
specific legislation, for dog bite prevention. (J Am Vet Med Assoc 2013;243:1726–1736)

D og bite–related injury has been viewed as a prevent-
able public health problem. Although extremely
rare events, human DBRFs have assumed a dispropor- BSL
ABBREVIATIONS
Breed-specific legislation
tionate role in the discussion of prevention and public DBRF Dog bite–related fatality
understanding of the much larger issue and far more
frequent event of nonfatal injuries from dog bites.1,2 ascertainment but still relied on media reports, which
Two early case series3,4 of DBRFs set the stage for use may be impossible to verify for completeness and ac-
of media reports as sources of data for analysis. Sub- curacy, to characterize DBRFs during the periods 1979
sequently, 4 related and highly influential reports in- to 1988,5 1989 to 1994,6 1995 to 1996,7 and 1979 to
corporated national mortality rate data to improve case 1998.8
Of the factors related to dog bites reported in the
From the Center for Animals and Public Policy, Department of Envi-
ronmental and Population Health, Cummings School of Veterinary
media as well as in scientific literature, the breed of dog
Medicine, Tufts University, North Grafton, MA 01536 (Patronek); has come to dominate public policy discussions about
Sue Binder Consulting Inc, 3958 Preston Ct NE, Atlanta, GA 30319 prevention and control. The undue emphasis on breed
(Sacks); the National Canine Research Council, 433 Pugsley Hill has contributed to a lack of appreciation of the owner-
Rd, Amenia, NY 12501 (Delise, Cleary); and the Center for Shelter ship and husbandry factors that more directly impact
Dogs at the Animal Rescue League of Boston, 10 Chandler St, Bos- dogs and the complex genetic factors that work in
ton, MA 02116 (Marder).
The National Canine Research Council supported the efforts of Karen
combination with husbandry to influence a dog’s be-
Delise from 2006 to 2011 for assembly of case reports and data ab- havior and responses to a given set of stimuli. This is
straction and Kara Gilmore, JD, for assistance with data abstraction unfortunate because even studies that relied on media
and validation from case reports. accounts and described the reported breeds reiterated
Donald Cleary is Director of Communications and Publications at the the importance of a more nuanced understanding of
National Canine Research Council and Treasurer of Animal Farm the circumstances leading to DBRFs and dog bites in
Foundation, parent organization of the National Canine Research
Council.
general.5–8 More recently, the advent of commercially
Presented in part as an oral presentation at the AVMA Annual Con- available DNA technology,a along with studies demon-
vention, Chicago, July 2013. strating the unreliability of visual breed identification
Address correspondence to Dr. Patronek (gary.patronek@tufts.edu). of mixed-breed dogs of known parentage9 and dogs of

1726 Scientific Reports JAVMA, Vol 243, No. 12, December 15, 2013
undocumented heritage,10–13 has cast further doubt on As a completeness check for DBRFs occurring from
the accuracy of news accounts and published reports 2000 to 2007, we used national death data, searching for

SMALL ANIMALS
of studies that relied on third-party reporting of breed. deaths with the International Classification of Disease
Indeed, what is striking is the consistency with Revision 10 (ICD-10) code W54 (bitten or struck by
which experts agree that dog bites cannot be adequately dog) as the underlying or contributory cause of death.
understood by examining single factors in isolation.14–22 For deaths identified in media reports but missing from
Furthermore, major professional bodies (eg, veterinary the national death data (ie, not coded as W54 [approx
associations in the United States21,22 and Europe,23,24 the 5 cases/y]), we used confirmation from the coroner or
American Bar Association,25 the National Animal Con- medical examiner as the criterion for inclusion. When
trol Association,26 and major humane organizations27,28) cases were listed in the national death reports but not
have not recommended single-factor solutions such as identified through media reports, this was often because
BSL (ie, enacting regulations that either prohibit dogs the cause of death was due to an excluded cause (eg,
on the basis of presumed breed or appearance or that an infection following a dog bite). For DBRFs occur-
impose additional requirements and expense with re- ring after 2007, this cross-check was no longer possible
spect to their keeping) as dog-bite prevention strate- because national death reporting suppressed identifiers
gies. It has been shown mathematically that BSL is un- that allowed such cross-checks to occur.
likely to be effective29; moreover, in a recent Canadian
study,30 there was no significant reduction in hospital- Data sources—The primary source of the data was
ization rates for dog-bite injury in communities before law enforcement agencies. The primary investigator
and after BSL was introduced. Nevertheless, BSL has (usually a homicide detective or other law enforcement
been promoted as an effective single-factor solution to officer) who interviewed witnesses, performed a de-
the problem of dog bites.31 Accordingly, some commu- tailed examination of the scene, compiled case reports,
nities have enacted BSL in the hope of improving public and obtained an in-depth narrative account of the in-
safety, potentially ignoring other more policy-relevant vestigation was contacted. In cases where the investiga-
factors and diverting resources from more effective pre- tion resulted in criminal charges, the investigator could
vention measures. only be interviewed after the case was closed. When
To improve the evidence base for understanding law enforcement investigators were unable to provide
and prevention of dog bites, the purpose of the study information through interviews, attempts were made
reported here was to examine potentially preventable to obtain police reports or to locate or interview other
factors in DBRFs on the basis of data from sources that sources. Attempts were made to obtain all other docu-
were more complete, verifiable, and accurate than media mentation that might be relevant to the case (eg, ani-
reports used in previous studies. Our intent was to ana- mal control bite reports, autopsy reports, crime scene
lyze data from previously unused sources (ie, in-depth photos, and photographs of the dog). Because a DBRF
investigations based on police reports and homicide in- may involve criminal liability on the part of a person
vestigations as well as coroner reports, animal control re- or persons, investigators initially determine either that
ports, and photographs); examine previously unreported criminal charges are not applicable, in which case their
behaviorally relevant and potentially policy-relevant fac- investigation closes quickly (eg, weeks to months),
tors associated with the victims, the dogs, the husbandry or that criminal charges may be applicable, in which
of the dogs, and the situational factors attendant to these case their investigation is more protracted (months to
incidents; describe the co-occurrence of these factors; years). Contact with the investigator was maintained
and characterize the reliability and accuracy of breed at- for the duration of the case, and new facts were ob-
tribution in media accounts of DBRFs. tained as they became available. During the study, in-
formation was compiled over a sufficiently long period
Materials and Methods for the entire range of available facts surrounding an
incident to have come to light.
Case ascertainment and definition—We attempt-
ed to identify all DBRFs in the United States during the Definition of variables—With respect to the dece-
10-year period from 2000 to 2009. A DBRF was defined dent’s relationship to a dog (or dogs), an owner was de-
as a death resulting from the mechanical trauma of fined as an adult with an established relationship with
a dog bite. Persons dying of causes such as infection a dog who provided care and maintained custody of the
following a dog bite or other trauma associated with dog for ≥ 90 days. A familiar relationship was defined
a dog-related incident (eg, a fall) were not consid- as an established positive relationship with the dog
ered DBRFs in this study. Initially, cases were identi- other than owner or primary caretaker (eg, someone
fied through media reports via a daily Internet searchb who is regularly present and familiar to the dog, such
with the following terms: dog bite, dog mauling, dog as a spouse, parent, child, other relative, or roommate,
mauled, dog attack, dog bite injuries, dog bite death, and who regularly interacts with the dog in positive and
and fatal bites. Investigation of cases and collection of humane ways); an incidental relationship was defined
data commenced as soon as a case was identified and as an association with the dog other than owner or pri-
were conducted prospectively beginning in 2000 with mary caretaker (eg, someone who is regularly present
follow-up on existing cases continuing through Decem- at the home, such as a spouse, parent, child, other rela-
ber 2011. In approximately 20 cases involving dog bites tive, or roommate, and who does not regularly inter-
where the cause of death was not clearly identified in act with the dog in positive and humane ways); and no
the media reports, we contacted the relevant medical established relationship was defined as a visitor to the
examiner or coroner to confirm the cause of death. home, an intruder to property, or a passerby. Victims

JAVMA, Vol 243, No. 12, December 15, 2013 Scientific Reports 1727
were deemed unable to interact appropriately with the connection with incident (yes, no, or unknown); sta-
dog if they were < 5 years of age or they had limited tus of dog in household (resident dog, family dog, or
SMALL ANIMALS

mental or physical capacity that increased their vulner- undetermined [evidence of human-canine relationship
ability (eg, dementia, alcohol intoxication, impairment not available or inconclusive]); typical housing of dog
from drugs, or uncontrolled seizure disorders). (chained, confined [kennel, shed, or pen in yard], loose
The status of a dog in a household was differenti- in fenced yard, loose in unfenced yard, indoor isola-
ated as either a resident dog or family dog. A resident tion [basement, garage, porch, laundry room, or crate],
dog was a dog, whether confined within the dwelling regular roaming loose off owner’s property, inside home
or otherwise, whose owners isolated them from regu- and not in isolation, indoor and outdoor, or unknown);
lar, positive human interactions. A family dog was a location of incident with respect to property where dog
dog whose owners kept them in or near the home and normally resided (off property, on property, both [ran
also integrated them into the family unit, so that the off property to attack victim], or unknown); duration
dogs learned appropriate behavior through interaction of dog’s residence on property if incident occurred on
with humans on a regular basis in positive and humane resident property (≤ 90 days, > 90 days, unknown, and
ways. not applicable [ie, off-property incident]); number of
Evidence that an owner allowed the dog to be a dogs known to have been involved in incident (1 dog, 2
danger to others (eg, previous bite incidents and run- dogs, 3 dogs, ≥ 4 dogs, or unknown); sex of dog or dogs
ning at large) was classified as mismanagement. A his- involved (male, female, both male and female, or un-
tory of neglect by the owner included instances of dogs known); reproductive status of dog or dogs (spayed or
not given access to shelter, food, water, or shade and castrated, sexually intact, both spayed or castrated and
dogs with untreated medical conditions. More extreme sexually intact, and unknown); breeding status of sexu-
events (eg, severe starvation, seemingly more deliberate ally intact dog or dogs involved in incident (not appli-
than simple neglect; an owner witnessed beating a dog cable [ie, dogs that are neutered or do not match other
previously; an owner sexually abusing a dog; an owner categories]; female in estrus; pregnant female; sexually
using a dog for dog fighting; or evidence of deliberate intact female with puppies; sexually intact female with
physical punishment or deprivation) were classified as subadult offspring; sexually intact male in vicinity of
owner abuse. For example, an owner bragged that after female in estrus, pregnant, or with puppies; both sexu-
his dogs had eaten food off the stove, “as punishment ally intact male and female; or unknown).
he fed the dogs dish soap for a week; no dog food, just To verify the coding categories and definitions
dish soap.” were understandable and repeatable, 2 individuals
(KMD and Kara Gilmore, JD) separately coded 20 case
Coding and verification—A standardized instru- reports and compared results. Based on discrepancies
mentc for abstracting information from the case report and problems identified, the form was revised and the
narratives was developed after a review of scientific same 2 individuals recoded the same 20 case reports,
literature and extensive discussion, with the intent to plus an additional 30 new cases. For the 19 variables
capture basic human and dog demographic information coded with 3 to 9 possible assignments of value, there
as well as environmental and situational variables that was exact agreement in value assignment in 915 of 950
would be behaviorally relevant from a dog’s perspec- (96%) cells. A third person (ARM) coded a sample of
tive. Categories were defined and coded as follows: vic- 20 case reports, and there was exact agreement in value
tim’s age (< 90 days, 3 to < 12 months, 1 to 4 years, 5 assignment in 355 of 380 (93%) cells. The final coding
to 9 years, 10 to 14 years, 15 to 69 years, or > 69 years); of the remaining case narratives was done by 1 person
victim’s gender (male or female); victim’s relationship (KMD).
to dog (none, familiar, incidental, owner or primary
caretaker, or unknown); duration of ownership on date Reliability and accuracy of breed identifications—
of incident (≤ 90 days, > 90 days, or unknown); oc- It should be noted that the source of breed descriptors
currence of bite in presence of owner or primary care- in media reports is usually unknown, potentially be-
taker (yes, no, or unknown); presence of able-bodied ing neighbors, first responders, or other witnesses who
person able to intervene on behalf of the victim at the may or may not have any first-hand knowledge of the
time of the incident (yes, no, or unknown); victim’s dog or dogs involved in an incident. Homicide detec-
vulnerability increased on the basis of age or limited tives typically made no independent determination of
mental or physical capacity (no [ie, victim able to as- breed for inclusion in their reports. We defined a valid
sist in the interaction via perception or communication determination of breed as documented pedigree, par-
between a dog and a human; persons ≥ 13 years of age], entage information, or results of DNA analysis. With
yes [ie, children < 5 years of age; cognitive impairment the understanding that the number of such cases would
due to age, mental disability, physical disability, alco- be limited, we also allowed for agreement of news ac-
hol or drug-related intoxication, or seizures], possibly counts, animal control assessment, and the photo-
[ie, victim possibly unable to interact appropriately {eg, graphic evidence for a given dog involved in a DBRF to
children 5 to 12 years of age or persons with cogni- conclude that it was reasonable to identify the dog as a
tive impairment due to age or other mental disability, purebred dog. In cases without pedigree information,
physical disability, alcohol or drug-related intoxication, parentage, DNA test results, or photographic evidence,
or seizures}]), or unknown); evidence of animal abuse validity of breed attributions could not be determined.
or neglect (yes, no, or unknown); owner mismanage- As a second level of analysis and to provide additional
ment of dog (yes, no, or unknown); criminal charges information about the reliability of media reports, the
filed against owner, parent, or primary caretaker in concordance of the reported breed descriptors among

1728 Scientific Reports JAVMA, Vol 243, No. 12, December 15, 2013
sources was assessed, with the understanding that it software package.d Descriptive statistics were compiled
would still be very difficult to know whether the as- and cross-tabulations were performed to explore re-

SMALL ANIMALS
signed breed was correct even if there was agreement lationships between variables. Co-occurrence among
among sources. factors was examined with respect to factors that we
Concordance was defined on the basis of both a believed had independent effects and minimal opportu-
strict and expanded definition. First, for the strict sce- nity for overlap in definition (victim having no familiar
nario, concordance was defined as an exact match in the relationship to the dog, no able-bodied person being
reported breed descriptor between 2 accounts. There- present, victim being compromised in ability to interact
fore, if one account reported a purebred dog (eg, Rott- appropriately with the dog, dog being a resident dog
weiler) and another reported the same dog as mixed instead of a family dog, owner failing to have the dog
breed (eg, Rottweiler–German Shepherd Dog mix), the spayed or castrated, evidence of mismanagement of dog
reports were considered discordant (not a match). For by owner, and owner having a history of abuse or ne-
the expanded definition of concordance, breed descrip- glect of dog). Fatal bite rates per 1 million person-years
tors did not need to be exact matches. For example, if were calculated on the basis of intercensal estimates.41
one account reported a purebred dog (eg, Rottweiler) Fatal bites per 1 million dogs were calculated for 2
and another reported the same dog as a mixed breed years (2001 and 2006)42,43 when pet survey ownership
that included that pure breed (eg, Rottweiler–German data were available and then the mean was calculated.
Shepherd Dog mix), it was considered to have an over-
lap of 1 breed descriptor and was therefore concordant Results
by the expanded definition.
Pit bull–type dogs posed a special challenge be- Primary sources—Law enforcement sources (ho-
cause this colloquial designation is not a breed per se micide detectives, chiefs of police, sheriffs, or other
but a descriptor of a heterogeneous group whose mem- investigators) were interviewed with regard to 177 of
bership includes various purebred dogs and presumed the 256 (69.1%) DBRFs. Animal control officers were
mixes of breeds; this descriptor varies according to the interviewed with regard to 44 of 256 (17.2%) DBRFs.
definition used in various statutes and ordinances and Other persons familiar with the cases (eg, veterinarians,
the opinions of the observer.32–40 The 3 breeds most prosecutors, owners, and witnesses) were interviewed
commonly grouped under the term pit bull in US BSL with regard to 24 of 256 (9.4%) DBRFs. For 11 (4.3%)
are American Pit Bull Terrier, American Staffordshire cases, no primary source could be interviewed but 2
Terrier, and Staffordshire Bull Terrier. Thus, for our of these DBRFs were reported extensively in the media
strict definition to be concordant, the terms used in dif- and were the subject of high-profile trials.
fering reports had to be: pit bull, pit bull terrier, Ameri-
can Pit Bull Terrier, American Staffordshire Terrier, or Frequency of fatal bites—Fatal dog bites were ex-
Staffordshire Bull Terrier (without the term mix). Thus, tremely rare throughout the 10-year period of study,
pit bull and American Staffordshire Terrier would be with a mean of 25.6 events/y in an annual human pop-
concordant, but pit bull and pit bull mix would be dis- ulation of approximately 295.5 million and an annual
cordant, as would American Staffordshire Terrier and dog population of approximately 68.8 million. This cor-
American Staffordshire Terrier mix. For the expanded responded to approximately 0.087 fatal bites/1,000,000
definition, concordances related to pit bull–type dogs person-years and 0.38 fatal bites/1,000,000 dogs in the
were considered when reported as pit bull, pit bull ter- United States.
rier, pit bull mix, pit bull terrier mix, American Pit Bull
Terrier, American Staffordshire Terrier, Staffordshire Victim-related factors—Nearly half (116/256
Bull Terrier, or any alleged mix thereof. [45.3%]) of victims were < 5 years of age, and a slight
Single dog incidents and multiple dog incidents majority (140/256 [54.7%]) were male (Table 1). Only
were analyzed separately. For multiple dog incidents, 17 (6.6%) victims were established owners; most vic-
we truncated those studied to events involving 2 to 6 tims (218/256 [85.2%]) either had an incidental rela-
dogs because some DBRFs involved an unknown num- tionship with the dog or no relationship to the dog. In
ber of dogs or dogs that could not be located (hence 143 of 256 (55.9%) DBRFs, the victim was deemed un-
lacked an animal control assessment). Discordance able to interact appropriately with the dog and, in an-
rates for breed reports from differing sources were cal- other 55 (21.5%) instances, deemed possibly unable to
culated as per 100 dogs. interact appropriately (eg, children aged 5 to 12 years
Finally, in cases without documented pedigree, or persons with cognitive impairment due to age or
parentage, or DNA information but where photographs other mental disability, physical disability, intoxication
of the dog or dogs involved were available, a veterinary [alcohol or drugs], and seizures).
behaviorist (ARM), who was unaware of the breed de- Among the 143 DBRFs where the victim was
scriptor used in the media or animal control reports, deemed unable to interact appropriately with the dog,
attempted to determine whether the dog could reason- this inability was due to age (< 5 years) in 116 (81.1%)
ably be described as a recognized purebred dog but did cases. However, of the remaining 27 victims whose abil-
not attempt to guess at possible breed mixes. Concor- ity to interact was compromised, 24 were persons ≥ 15
dance with the media report was assigned on the basis years. Most of these older individuals (16/24 [66.7%])
of the expanded definition. were adults compromised as a result of drug or alco-
hol intake. Five others were compromised because of
Statistical analysis—Data were entered into an Alzheimer’s disease, dementia, or an uncontrolled sei-
electronic spreadsheet and imported into a commercial zure disorder. Increased vulnerability as a result of be-

JAVMA, Vol 243, No. 12, December 15, 2013 Scientific Reports 1729
Table 1—Victim-related and situational factors involved in 256 Table 2—Dog-related factors involved in 256 DBRFs in the United
DBRFs in the United States (2000–2009). States (2000–2009).
SMALL ANIMALS

Variable No. (%) of DBRFs Variable No. (%) of DBRFs
Age Weight
< 90 d 21 (8.2) < 23 kg 13 (5.1)
90 d–< 1 y 9 (3.5) 23–45 kg 203 (79.3)
1–4 y 86 (33.6) > 45 kg 19 (7.4)
5–9 y 35 (13.7) Multiple weights 7 (2.7)
10–14 y 9 (3.5) Unknown 14 (5.5)
15–69 y 60 (23.4) Sex of dogs involved
> 69 y 36 (14.1) Male exclusively 148 (57.8)
Female exclusively 26 (10.2)
Gender Both male and female 76 (29.7)
Male 140 (54.7) Unknown 6 (2.3)
Female 116 (45.3) No. of dogs involved
1 148 (57.8)
Relationship to dog* 2 59 (23.0)
Owner or primary caretaker 17 (6.6) 3 13 (5.1)
Familiar relationship 16 (6.3) ≥4 23 (9.0)
Incidental relationship 28 (10.9) Unknown 13 (5.1)
No relationship to dog 190 (74.2)
Unknown 5 (2.0) Sex status of dogs
Spayed or castrated only 18 (7.0)
Ability to interact appropriately with dog Sexually intact only 212 (82.8)
compromised in some manner† Both spayed or castrated and sexually intact 4 (1.6)
Yes 143 (55.9) Unknown 22 (8.6)
No 58 (22.7)
Possibly 55 (21.5) Reproductive status of dogs at time of incident
Female dog in estrus, pregnant, or with puppies 18 (7.0)
Presence of able-bodied adult able to intervene Sexually intact male involved in incident in the 25 (9.8)
at time of incident vicinity of female dog in estrus, pregnant,
Yes 28 (10.9) or with puppies
No 223 (87.1) Sexually intact male with sexually intact female 40 (15.6)
Unknown 5 (2.0) (both involved in incident)
Unknown 103 (40.2)
Data regarding DBRFs were identified from media reports, Not applicable (spayed or castrated dogs or 70 (27.3)
and detailed histories were compiled on the basis of reports from sexually intact dogs with none of the
homicide detectives, animal control reports, and interviews with reproductive status factors present)
investigators.
*A familiar relationship was defined as an established positive
relationship with the dog by someone other than the owner or pri-
mary caretaker (eg, someone who is regularly present and familiar
to the dog, such as the owner or primary caretaker’s spouse, parent, dogs, whereas over half the deaths (63/96 [65.6%]) in
child, other relative, or roommate, and who regularly interacts with persons ≥ 15 years of age involved multiple dogs. Re-
the dog in positive and humane ways); an incidental relationship
was defined as an association with the dog by someone other than gardless of whether all or most of the dogs participated,
the owner or primary caretaker (eg, someone who is regularly pres- there was > 1 dog kept either on the premises or in the
ent at the home, such as the owner or primary caretaker’s spouse, immediate vicinity of the incident in 210 (82%) cases;
parent, child, other relative, or roommate, and who does not regu-
larly interact with the dog in positive and humane ways); and no in 19 DBRFs, there was only 1 dog kept on the premises
established relationship was defined as a visitor to the home, an or in the immediate vicinity of the incident, and for 27
intruder to property, or a passerby. †Victims were deemed unable DBRFs, the number of dogs kept on the premises or in
to interact appropriately with the dog if they were < 5 years of age
or they had limited mental or physical capacity that increased their the immediate vicinity of the incident was unknown.
vulnerability (eg, dementia, intoxication [alcohol or drugs], or un- Most cases (216/256 [84.4%]) involved dogs
controlled seizure disorders). whose owners had not had them spayed or castrated.
Of the nearly one-third (76/256 [29.7%]) of DBRFs in-
volving both male and female dogs, almost all involved
ing unable to interact appropriately with a dog was an a sexually intact dog (70/76 [92.1%]). Only 18 of 256
important factor because, in 223 of 256 (87.1%) cases, (7.0%) DBRFs involved only dogs that were neutered.
no able-bodied person was near enough to the victim to Spayed females were known to be involved in only 2 (<
be able to intervene. 1%) DBRFs. Among the 195 DBRFs involving resident
dogs, their owners had failed to have the dogs neutered
Dog-related factors—The weight range of most in 182 (93.3%) cases. Among the 40 DBRFs involving
dogs was 23 to 45 kg (approx 50 to 100 lb; Table 2). family dogs, the owners had failed to have the dogs
Most DBRFs (224/256 [87.5%]) involved male dogs, ei- neutered in 24 (60%). In 83 cases, owners maintained
ther single or multiple male dogs (148/224 [66.1%]), dogs in reproduction (eg, a female in estrus, a pregnant
or male dogs together with female dogs (76/224 female, or a female with nursing or young puppies pres-
[33.9%]). Incidents involving only male dogs were 5 ent) or in circumstances conducive to reproduction (eg,
times as frequent as incidents involving only female a sexually intact male being kept with a sexually intact
dogs. In slightly more than half of the 256 DBRFs (148 female). Not all of these dogs were deemed by the in-
[57.8%]), only a single dog was involved. When a sin- vestigators to be involved in the DBRF despite being in
gle dog was involved, it was a male dog in 127 of 148 the general vicinity; however, the presence of dogs with
(85.8%) incidents. Most (26/30 [86.7%]) deaths among these reproductive issues could have influenced the be-
infants (< 1 year of age) were attributable to single havior of the dogs involved in the bite.

1730 Scientific Reports JAVMA, Vol 243, No. 12, December 15, 2013
In only 57 of the 256 (22.3%) DBRFs did the own- tion. Results of review of photographs of 66 other dogs
ers know or were investigators able to determine with by a veterinary behaviorist agreed with news reports of

SMALL ANIMALS
any degree of reliability the age of the dog. In only 39 purebred status for 9 of 66 (13.6%) dogs.
of the 256 (15.2%) incidents was it possible to assign a For multiple dog cases, pedigree documentation,
single, distinct function to the dog. Therefore, given the parentage, or DNA information was available for 28
extent of missing data for these 2 variables, detailed re- dogs. These data were discordant with media reports
sults for categories of age and function are not reported. for 7 of 28 (25.0%) cases on the basis of the strict breed
It was not possible to precisely determine the to- definition and 0 of 28 (0%) cases on the basis of the ex-
tal number of dogs involved in these 256 DBRFs be- panded breed definition. On review of photographs of
cause, in some cases when multiple dogs were present, 95 other dogs, the veterinary behaviorist could confirm
the total numbers were not reported or it was simply the media report of purebred status for only 3 of 95
unknown exactly how many dogs were involved. Con- (3.2%) dogs but did not attempt to guess breed mixes
servatively, we estimated at least 455 individual dogs. when a dog did not appear to conform to the breed stan-
dard for purebred dogs. It should be noted that 354 of
Determination of breed—To examine breed of 393 (90.1%) dogs that were assigned a breed descriptor
dogs, we used media reports, animal control reports, were assigned a single breed descriptor (ie, not reported
pedigree, parentage information, or results of DNA anal- as a mixed breed) in at least 1 media report.
ysis, when available. To evaluate the reliability of breed
determinations reported by the media, we attempted Table 3—Husbandry-related and other factors involved in 256
to use concordance among reporting sources of breed DBRFs in the United States (2000–2009).
descriptors, recognizing that even with concordance,
Variable No. (%) of DBRFs
sources could still be in error, particularly when dogs
were of mixed breeding. For single dog incidents (148 Duration of ownership
incidents), on the basis of the strict definition (exact ≤ 90 d 28 (10.9)
> 90 d 200 (78.1)
match), breed descriptors in media reports were discor- Unknown 28 (10.9)
dant for 32 of 148 (21.6%) dogs; animal control or local Status of dog in household
law enforcement assessment of breed differed from the Resident dog* 195 (76.2)
Family dog 40 (15.6)
media account for 45 of 129 (34.9%) dogs. On the basis Unknown 21 (8.2)
of the expanded definition (any agreement between al-
leged breeds and mixes), breed descriptors among me- Location in which dog was kept
Home 20 (7.8)
dia reports were discordant for 19 of 148 (12.8%) dogs; Indoors and outdoors 37 (14.5)
animal control or local law enforcement assessment of Loose in fenced yard 35 (13.7)
breed differed from the media account for 18 of 129 Loose in unfenced yard 11 (4.3)
Roaming 30 (11.7)
(14.0%) dogs. Pen 19 (7.4)
For multiple dog incidents (96 deaths involving On a chain 74 (28.9)
256 dogs), on the basis of the strict definition (exact Indoor isolation 14 (5.5)
match), breed descriptors in media reports were discor- Unknown 16 (6.3)
Location of dog at time of incident
dant for 92 of 253 (36.4%) dogs; animal control or local On owner’s property 190 (74.2)
law enforcement assessment of breed differed from the Off owner’s property 51 (19.9)
media account for 94 of 217 (43.3%) dogs. On the basis Both on and off property 13 (5.1)
Unknown 2 (0.8)
of the expanded definition (any agreement between al-
leged breeds and mixes), breed descriptors among me- Evidence of mismanagement by owner†
dia reports were discordant for 43 of 253 (17.0%) dogs; Yes 96 (37.5)
No 112 (43.8)
animal control or local law enforcement assessment of Unknown 48 (18.8)
breed differed from the media account for 24 of 217 History of neglect or abuse by owner‡
(11.1%) dogs. Yes 54 (21.1)
No 170 (66.4)
Breed was inaccurately represented in the media in Unknown 32 (12.5)
other ways. For example, 7 deaths were originally re-
ported by the media as involving multiple dogs; further Owner present at time of bite
Yes 12 (4.7)
investigation revealed that 8 dogs were not involved No 223 (87.1)
and the deaths were actually single dog incidents. For Owner was victim 17 (6.6)
another 9 deaths reported by the media as involving Unknown 4 (1.6)
multiple dogs, later investigation revealed that although Criminal charges filed
Yes 67 (26.2)
multiple dogs were involved, 13 media-implicated dogs No 177 (69.1)
were not involved. Thus, 16 of 256 (6.3%) deaths in- Unknown 12 (4.7)
volved inaccurate media reporting of the number of in- *A resident dog was a dog kept isolated from regular, positive
dividual dogs involved, yet all of these dogs had media- human interactions. †Evidence that an owner allowed the dog to be
reported breed descriptors. a danger to others (eg, previous bite incidents and running at large)
With respect to pedigree or results of DNA analy- was classified as mismanagement. ‡Neglect by the owner included
instances of dogs not given access to shelter, food, water, or shade
sis for single dog cases, pedigree documentation, par- and dogs with untreated medical conditions; abuse was classified
entage, or DNA information was available for 19 dogs. as more extreme events (eg, severe starvation, seemingly more
These data were discordant with media reports for 7 of deliberate than simple neglect; an owner witnessed beating a dog
previously; an owner sexually abusing a dog; an owner using a dog
19 cases on the basis of the strict breed definition and for dog fighting; or deliberate physical punishment or deprivation).
0 of 18 cases on the basis of the expanded breed defini-

JAVMA, Vol 243, No. 12, December 15, 2013 Scientific Reports 1731
Overall, breed status was assigned for dogs in- allowed to roam (30/195 [15.4%]). There were no in-
volved in 45 of 256 (17.6%) DBRFs from documented stances in which resident dogs and family dogs were
SMALL ANIMALS

pedigree, parentage information, or DNA test results jointly involved in a DBRF.
or on the basis of concordance among media breed de- In 96 of 256 (37.5%) DBRFs, there was evidence
scriptor, animal control breed descriptor, and the vet- that the owner or caretaker had foreknowledge of either
erinarian-assigned breed from a photograph. These 45 prior dangerous action by the dog or had repeatedly al-
DBRFs involved 20 recognized dog breeds, including 2 lowed the dog to run loose. In 54 of 256 (21.1%) cases,
dogs of known mixed breed. there was evidence of prior abuse or neglect of the dog.
Nearly three-quarters (190/256 [74.2%]) of the deaths
Husbandry-related factors—Most DBRFs involved occurred on the owner’s property, and only 51 deaths
dogs known to be owned > 90 days (200/256 [78.1%]), occurred entirely away from the owner’s property. In
and only a small proportion involved dogs known to 32 of 51 (62.7%) off-property incidents versus 55 of
be owned ≤ 90 days (28/256 [10.9%]; Table 3). Over 190 (29%) on-property incidents, there was a history
three-quarters of cases (195/256 [76.2%]) involved of mismanagement of dogs by owners. Past misman-
dogs kept by their owners as resident dogs rather than agement was also associated with the number of dogs
as family dogs. In incidents involving resident dogs, involved in an incident. That is, where there had been
those dogs were kept in a manner that isolated them past mismanagement by the owner, multiple dogs were
from the humans in the family, such as chained (74/195 involved in 54 of 96 (56.3%) DBRFs; where there had
[37.9%]); kept isolated in a fenced area, an outdoor been no documented prior mismanagement, multiple
pen, or an isolated indoor area (68/195 [34.9%]); or dogs were involved in 27 of 112 (24.1%) DBRFs.
Criminal charges for misdemeanors or felonies (in
addition to animal control violations) were filed for 67
of 256 (26.2%) DBRFs. Nearly half (47/96 [49.0%])
of owners with a history of dog mismanagement were
criminally charged, compared with only 13 of 112
(11.6%) owners without such a history. Of the 67
criminal charges, legal proceedings resulted in convic-
tions (sentences of 1 to 15 years) for 34 and dismissed
charges, mistrials, or sentences of probation or < 1 year
for 33.
Many of the factors described regarding the vic-
tim, dog, and husbandry were co-occurrent in a large
number of DBRFs (Figure 1). Co-occurrence of ≥ 4 of
these factors was evident in more than three-quarters
(206/256 [80.5%]) of cases.
Discussion
These study data were obtained over many years of
Figure 1—Co-occurrence of preventable factors in 256 DBRFs in
the United States from 2000 to 2009. Values above each bar indi- investigation and collection from multiple sources (eg, in-
cate the percentages; values in parentheses indicate the number of terviews with and police reports from homicide investiga-
cases. Data regarding DBRFs were identified from media reports, tors, interviews with animal control personnel, and multi-
and detailed histories were compiled on the basis of reports from ple sources of written documentation). In our opinion, the
homicide detectives, animal control reports, and interviews with
investigators. Numbers over the bars indicate the percentage of present study represents the most comprehensive analysis
cases (actual number of cases) in which 1 or more of the following of factors—behaviorally relevant factors in particular—as-
factors were present: victim having no familiar relationship to the sociated with dog bites to date. Personal interviews with
dog, no able-bodied person being present during incident, victim
compromised in ability to interact appropriately with the dog, dog credible investigators were successfully conducted in 221
being a resident dog (ie, kept isolated from regular, positive human of 256 (86.3%) cases. During this data-gathering process,
interactions) instead of a family dog, owner failing to have the dog we found that law enforcement personnel provided first-
spayed or castrated, evidence of mismanagement of dog by owner,
and owner having a history of abuse or neglect of dog. A familiar hand information not reported in the media and often
relationship was defined as an established positive relationship with identified errors of fact in the media reports.
the dog by someone other than the owner or primary caretaker (eg, In the present study, the most striking finding was
someone who is regularly present and familiar to the dog, such as
the owner or primary caretaker’s spouse, parent, child, other rela- the co-occurrence of multiple factors potentially un-
tive, or roommate, and who regularly interacts with the dog in posi- der the control of dog owners: isolation of dogs from
tive and humane ways). Victims were deemed unable to interact positive family interaction and other human contact;
appropriately with the dog if they were < 5 years of age or they had
limited mental or physical capacity that increased their vulnerability mismanagement of dogs by owners; abuse or neglect
(eg, dementia, intoxication [alcohol or drugs], or uncontrolled seizure of dogs by owners; dogs left unsupervised with a child
disorders). Evidence that an owner allowed the dog to be a danger or vulnerable adult who may be unfamiliar to the dog;
to others (eg, previous bite incidents and running at large) was clas- and maintenance of dogs in an environment where they
sified as mismanagement. Neglect by the owner included instances
of dogs not given access to shelter, food, water, or shade and dogs are trapped, neglected, and isolated and have little con-
with untreated medical conditions; abuse was classified as more trol over either the environment or choice of behavior.
extreme events (eg, severe starvation, seemingly more deliberate These conditions potentially predispose dogs to en-
than simple neglect; an owner witnessed beating a dog previously;
an owner sexually abusing a dog; an owner using a dog for dog fight- hanced territorial, protective, and defensive behaviors
ing; or deliberate physical punishment or deprivation). toward stimuli that occur commonly in everyday life.

1732 Scientific Reports JAVMA, Vol 243, No. 12, December 15, 2013
The most preventable incidents involved very young tive and nonthreatening manner that would allow the

SMALL ANIMALS
children left alone with dogs to whom they were un- dog not to fear children and to understand their pattern
familiar or toddlers allowed to wander off and encoun- of behaviors is likely to be afraid of them. A fearful dog
ter unfamiliar dogs. In at least 19 DBRFs, authorities will avoid stimuli that invoke the fear, but if unable to
considered the lack of supervision in such incidents so avoid, as when tied, may become aggressively defensive.
negligent that criminal charges were filed against the Maintained in this way, it is extremely unlikely that a
parent or caretaker. dog, notwithstanding its uninterrupted habitation on
When interpreting these incidents, it is critical to the same property, would have had the opportunity to
keep in mind what factors may be behaviorally relevant interact in positive and humane ways with humans, in-
from a dog’s perspective and how human decisions to cluding a child. Discouraging maintenance of dogs in
maintain, confine, and treat the dogs may predispose isolation from the family; stressing the importance of a
them to inflict a severe bite. Dogs that have not devel- secure, stable, predictable environment; and encourag-
oped a close relationship or bond with humans (ie, ing positive relationships with people may have consid-
resident dogs) generally act without relying on input erable preventive benefits.
from a human. Tópal et al44 reported that dogs living According to the 2007 AVMA Pet Ownership Sur-
in homes (in contrast to dogs living outdoors) devel- vey,48 62.2% of US dog-owning households have only
oped bonds with people and were more dependent on 1 dog, 24.8% have 2 dogs, 7.5% have 3 dogs, and 5.5%
their owners when solving tasks. In agreement with have 4 or more dogs. Yet, we found that in 210 of the
other studies,9,45,46 those authors concluded that the 256 (82%) DBRFs, there were multiple dogs either on
individual past experiences of dogs strongly influence or near the scene, regardless of whether > 1 dog was in-
their later social behavior with people.44 Appropriate, volved and whether all of the dogs present were owned
humane, and clear interactions with people provide by the same person. Appropriate management of dogs,
dogs with information about how to interact with hu- which is important in all situations, may be more chal-
mans in ways that are neither scary nor injurious to the lenging when multiple dogs and other complicating
dog or human. This can occur through daily interaction conditions are present. Furthermore, maintaining mul-
but cannot occur when dogs are reared apart from daily, tiple dogs that have no history of good and close rela-
freely offered (not while chained) human interactions. tionships with people, in conjunction with dogs being
The effect of that bond is that dogs that interact fre- in various reproductive conditions, may increase their
quently with humans read human signals well and are reactivity to certain stimuli, even those present in daily
encouraged to act on them accordingly. Dogs that are life.
deprived of human interaction or direction are denied In the present study, most DBRFs (224/256
access to accurate information about appropriate be- [87.5%]) involved a male dog, and most of those in-
haviors with humans. Consequently, dogs in stressful, cidents involved at least 1 dog that was sexually intact
potentially dangerous situations or when maltreated (216/256 [84.4%]). Several studies49–53 of aggression in
may behave in ways primarily to protect themselves. dogs have found that male dogs bite more frequently
Mirkó et al47 emphasized the importance of environ- than do female dogs, and male dogs that are sexually
ment in influencing the personality of individual dogs. intact bite more often than do those that are castrated.
Those authors found that the dogs’ environment had a Although it is unknown whether castration directly af-
stronger influence on personality than did genetically fects the incidence of aggression toward people, stud-
determined breed differences. ies54,55 have shown that castration decreases aggression
In the present study, the finding that most dogs toward other dogs. Overall and Love14 suggested that
were not recently acquired (ie, were owned > 90 days) testosterone may modulate behavior, and thus sexually
and therefore presumably were acclimated to their en- intact male dogs react more intensely, more quickly, and
vironment and to at least some of the people in it bears for a longer period of time. It is also possible that peo-
discussion. Adults, being familiar with the dog, may ple who desire protective dogs choose males and decide
assume this familiarity will be automatically extended not to have them castrated, expecting or encouraging
unto their children (unfamiliar to the dog) or to other any tendency to be protective or aggressive. It is easy to
unrelated children or adults. It is incorrect to assume envision that when sexually intact male dogs are raised
that because a dog has been around some people for a as resident dogs, tied outside, and left unsupervised,
period of time that the dog will feel comfortable around they could be even more likely to bite. In the present
all people in all circumstances. It may well be that an study, 182 of the 195 (93.3%) DBRFs associated with
unfamiliar child or adult entering the environment has resident dogs involved sexually intact dogs, whereas
changed the dog’s environment (introduced novelty rel- only 24 of the 40 (60%) DBRFs associated with family
evant to the dog) and perhaps the dog’s comfort level. dogs involved sexually intact dogs. This suggests that
For example, in 1 case, a 2-year-old child wandered owner failure to have their dog spayed or castrated may
over to a chained resident dog. This dog had had the co-occur with other factors that more directly influence
same owner for 12 years, and during that time, the dog a dog’s social competence.
was kept on a chain in the backyard during the summer The issue of breed merits special discussion be-
months and confined in the basement during the win- cause of its prominence in the scientific literature and
ter months. Thus, most of the time, the dog was sepa- influence on public policy. The data obtained in the
rated from the owner and other people and had little present study indicated 2 problems with media char-
opportunity for a healthy human-dog bond to develop. acterization of dog breeds: poor reliability and poor ac-
A dog that has not been exposed to children in a posi- curacy. One source of media error was the misclassifica-

JAVMA, Vol 243, No. 12, December 15, 2013 Scientific Reports 1733
tion of whether individual dogs are even involved in a history or acts of aggression, he or she may have had
SMALL ANIMALS

death, which by our estimate occurred in at least 6% of no further interest in pursuing a more detailed history.
the cases. By use of the strict definition of discordance, We were not able to contact or obtain an interview with
combination of single dog and multiple dog DBRFs the lead investigator for all DBRFs in the present study.
revealed that for the 401 involved dogs described in Photographs of the scene and the dogs were of vari-
> 1 media account, reported breed differed for 124 able quality. Media reports were collected primarily as
(30.9%); for 346 dogs with both media and animal con- a trigger to pursue information from primary sources
trol breed reports, breed differed for 139 (40.2%). By such as local law enforcement, and no attempt was
use of the expanded definition of discordance, reported made to comprehensively and systematically collect ev-
breed differed for 62 of 401 (15.5%) dogs described in ery media report associated with each DBRF; thus, the
> 1 media account and 42 of 346 (12.1%) dogs with discordance among media reports of breed, discordance
both media and animal control breed reports. Which- between media reports and animal control reports, and
ever definition of concordance is used, disagreement the number of dogs erroneously reported as being in-
occurs with sufficient frequency to cast doubt on the volved in a DBRF were all likely underestimated. Fi-
reliability of these reports as a source of information nally, it was not possible to explore owner-level socio-
about presumed breed. It is also important to remem- economic characteristics because these data were not
ber that, even when concordance was documented, this obtained by investigators. Future studies may wish to
does not mean the assessment of breed was valid (ie, consider such factors, but it is important to note that
correct); it simply means that 2 sources reported the as with dog-related factors, it is likely that owner-level
same information. According to media reports, 90.1% socioeconomic factors could be misleading when con-
of the dogs were characterized in at least 1 media re- sidered in isolation. Persons of all socioeconomic levels
port with a single breed descriptor and not as a mixed are able to be responsible dog owners, although it is
breed. This distribution is in contrast to the known dis- possible that animal control enforcement efforts and ac-
tribution of breeds in the general population of dogs; cess to veterinary care and other resources available to
population-based studies indicate that a large (approx support responsible ownership could well be different
46%) proportion of dogs are mixed breed,56 suggesting in different neighborhoods.
either that in media reports and perhaps animal con- Results of the present study were derived from new
trol reports, designation of breed is done very loosely and more extensive sources of data than those used in
without regard to mixed-breed status or that purebred previous studies5–8 of DBRFs. However, these data have
dogs were heavily overrepresented in DBRFs. The latter fully supported the recommendations in those study
conclusion seems unlikely to us, particularly in light of reports5–8 and of experts on the subject of dog bite–
the photographic evidence available. related injuries, including the AVMA Task Force on Ca-
The lack of concordance among breed descriptors nine Aggression and Human-Canine Interaction21 and
was not surprising because identification of the breed the CDC,58 who have consistently stressed the complex
composition of a dog of unknown heritage has been and multifactorial nature of dog bites and the need for
shown to be unreliable; this may reflect the diverse multiple approaches to address this complexity. The
appearance of offspring even from deliberate breed- present study findings also have supported recommen-
ing of known parents9 or, as revealed in more recent dations by the AVMA22 and others23–28 regarding the
studies,10–13 the fact that opinions (even those of animal inadvisability of single-factor solutions such as BSL,
professionals with years of experience) correlate poorly which may actually divert resources from more effec-
with each other and with results of DNA analysis. En- tive measures and regulations. For example, in Prince
forcement of BSL must therefore grapple with imprecise George’s County, Md, following enaction of BSL in
and subjective identification of dogs presumed subject 1997, a task force established in 2002 found that the
to regulation. Breed-specific legislation must also be cost to animal control for maintenance of banned dogs
viewed in light of study findings9,57 that indicate a lack was > $500,000 during a 2-year period.59
of correlation between behavior and physical pheno- Animal services programs that insist on responsible
type. This imprecision in breed assignment also brings ownership should be promoted and adequately funded.
into question the reliability of the breed information Information about dog behavior and bite prevention
used in previous studies5–8 of DBRFs, which were based must be disseminated to an audience that extends be-
solely on media reports of breed. yond animal care professionals. Maintenance of dogs in
The coding system used for abstracting informa- ways (ie, as family pets instead of as resident dogs that
tion from official reports and interviews, despite being are isolated from the family) that allow them to inter-
repeatable among different coders, nevertheless re- act regularly with humans in positive and humane ways
quires subjective assessment. The information available may help dogs learn to read human signals, understand
for each case varied, depending on officials’ interest in their meaning, and respond to them appropriately. As a
conducting an investigation and pursuing a criminal result, dogs would be less likely to be afraid of and de-
prosecution. Some information that might be highly fensive in the presence of unfamiliar people, including
relevant to an animal professional might not be report- children, because they have had positive experiences
ed by police investigators (eg, animal abuse or neglect); with their patterns of behavior.
therefore, those situations may be underreported. Most Given the disproportionate number of dog bites
detectives had little knowledge about dogs and relied occurring among children, it is critical to revisit exist-
on what owners or animal control personnel told them. ing recommendations concerning managing the inter-
If the case detective could not document a previous bite actions between children and dogs.21,60 Most children

1734 Scientific Reports JAVMA, Vol 243, No. 12, December 15, 2013
have never received dog bite prevention education,61 12. University of Florida College of Veterinary Medicine. Maddie’s
and lack of supervision is common in reports of dog Shelter Medicine Program. DNA and survey results: what kind of